Due to the high cost of gemstones and diamonds and the work involved in finishing them, it is desirable to determine, in advance, the optimal finished stone which can be cut from an uncut gemstone or diamond. In the past, this was done by eye by the individual who would work the gemstone or diamond, particularly in the case of a diamond. If an error was made, either more material than necessary was removed and wasted, or the entire stone had to be discarded.
Accordingly, with the increasing use of computers, a number of computerized systems were developed for examining gemstones and diamonds, and comparing the shape of the stone with a variety of pre-selected shapes in order to determine which is the best fit. This is generally accomplished by mounting the stone on a rotating dop or other holder, and scanning the rotating stone. According to one series of patents, the stone is lit from the rear, providing a silhouette of the stone, which is analyzed by the computer and compared with a number of silhouettes of finished stones. According to another series of patents, such as U.S. Pat. No. 4,417,564, the stone is scanned normal to the axis, so as to permit the computer to provide a three-dimensional image of the stone.
One particular problem which is not solved by conventional devices, especially those analyzing a silhouette, is the case of a reentrant or recess in the stone. While it is clear that any protrusions will be visible in the silhouette, a recess will not be visible, which results in many incorrect decisions regarding the proper working of stones.
One patent which purports to solve this problem is Israel Patent 66292 to Gersan Establishment. This patent describes a method of examining a gemstone which includes projecting a thin beam of light onto the stone, moving the beam relative to the stone, sensing the position where the beam strikes the stone, as viewed in a direction different from that in which the beam is projected, and determining a parameter of the stone making use of information derived from sensing that position. This patent suffers from a number of disadvantages. First, a thin beam of light is not sufficiently precise to provide accurate measurement of reentrants. Second, and more important, since most gemstones and diamonds are transparent and reflective, the beam of light will not be reflected in a way that it can be viewed by a camera which is located as illustrated in this patent.
Similarly, when three dimensional objects are to be scanned or measured, it is either difficult or very expensive to measure depressions or recesses in the surface of the object.
There is known a method of measuring distance known as structured light triangulation which is based on a laser as the light source. This method is used for robotic and computer vision systems. This method is not suitable for mapping the surface of a gemstone or diamond since their surfaces are either transparent or reflective and, thus, cannot be viewed by a camera.
Accordingly, there is a long felt need for an apparatus and method for examining an object, particularly a gemstone, which can rapidly and inexpensively provide a 3-dimensional image of the object, including mapping recesses and reentrants in the object.
According to the present invention, there is provided a method for examining an object including the steps of coating the object with a diffusing coating, determining the silhouette of the object in three dimensions, and using structured light triangulation to determine the location of any recesses in the surface of the object.
According to a preferred embodiment, the method includes the steps of coating the object with a diffusing coating, mounting the object on a rotating holder, illuminating the object from behind to create a silhouette, illuminating a line or grid on the object, preferably by means of a laser, scanning the object by means of a camera disposed in front of the object and at a predefined acute angle from the laser for, providing signals from the camera corresponding to the shape of the object, and generating an image of the object from the signals.
According to one embodiment of the invention, the step of coating includes electrochemical electro-less coating of the object.
According to another embodiment of the invention, the step of coating includes painting the object with a layer of between about 10 and 20 microns of paint.
According to yet another embodiment of the invention, the step of coating includes vacuum evacuation.
According to one embodiment of the invention, the steps of illuminating the object from behind and illuminating the object by means of a laser are carried out substantially simultaneously.
According to an alternative embodiment of the invention, the step of illuminating the object from behind is carried out before the step of illuminating the object by means of a laser.
There is also provided in accordance with the present invention an apparatus for examining a object including means for holding a object coated with a diffusing material, a first light source for illuminating the object from behind to create a silhouette, a second light source for illuminating a line or grid on the object, a camera disposed in front of the object and at a predefined acute angle from the second light source for scanning the object and providing signals corresponding to the shape of the object, and a processor for generating an image of the object from the signals.